Non-Canonical Jets-in-Crossflow

2003 ◽  
Author(s):  
Michael W. Plesniak
Keyword(s):  
Film Cooling ◽  
Particle Image ◽  
Vortex Pair ◽  
Structural Features ◽  
Complementary Information ◽  
Global Features ◽  
The Past ◽  
Jet Trajectory ◽  
Image Velocimetry ◽  
Counter Rotating Vortex Pair

This invited paper presents a review of research done over the past several years at Purdue on non-canonical jets-in-crossflow. It is a retrospective and an integrative compilation of results previously reported as well as some new ones. The emphasis is on jets emanating from “short” holes, with length-diameter ratios of one or less. These are non-canonical in the sense that the flow is unable to “adjust” to the hole, unlike that in case of a long hole in which fully developed pipe flow can be attained. This motivated by gas turbine film cooling applications. Experimental results acquired with Particle Image Velocimetry will be presented primarily, with some complementary information gained from RANS simulations of the flow. Many different aspects of the problem have been investigated, and in this paper the focus will be on structural features within the hole and in the developing jet and crossflow interaction. A significant result is that the in-hole vertical structures, depending on their sense of rotation, tend to augment or weaken the primary counter-rotating vortex pair. This impacts global features such a jet trajectory and spreading.

Noncanonical Short Hole Jets-in-Crossflow for Turbine Film Cooling

2005 ◽  
Vol 73 (3) ◽  
pp. 474-482 ◽  
Author(s):  
Michael W. Plesniak
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Pair ◽  
Structural Features ◽  
Global Features ◽  
Vortical Structures ◽  
Jet In Crossflow ◽  
Jet Trajectory ◽  
Image Velocimetry ◽  
Counter Rotating Vortex Pair

This paper presents a review of research done over the past several years at Purdue on non-canonical jets-in-crossflow. It is a retrospective and an integrative compilation of results previously reported as well as some new ones. The emphasis is on jets emanating from “short” holes, with length-diameter ratios of one or less. A canonical jet-in-crossflow configuration is one in which a fully developed jet issues from a long pipe fed by a large plenum, into a semi-infinite cross flow. The configuration presented here is noncanonical in the sense that jet issues from a short hole and thus the flow is unable to “adjust” to the hole, unlike the case of a long hole in which fully developed pipe flow can be attained. This is motivated by gas turbine film cooling applications. Experimental results acquired with particle image velocimetry will primarily be presented, with some complementary information gained from RANS simulations of the flow. Many different aspects of the problem have been investigated, and in this paper the focus will be on structural features within the hole and in the developing jet and crossflow interaction. A significant result is that the in-hole vortical structures, depending on their sense of rotation, tend to augment or weaken the primary counter-rotating vortex pair. This impacts global features such as jet trajectory and spreading.

scholarly journals Characteristics of helicopter engine exhaust through scaled experiments using stereoscopic particle image velocimetry

2020 ◽  
pp. 095441002096647
Author(s):  
Zhen Wei Teo ◽  
Wai Hou Wong ◽  
Zhi Wen Lee ◽  
Tze How New ◽  
Bing Feng Ng
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Vortex Pair ◽  
Stereoscopic Particle Image Velocimetry ◽  
Engine Exhaust ◽  
Freestream Velocity ◽  
Hot Air ◽  
Image Velocimetry ◽  
Air Blower ◽  
Counter Rotating Vortex Pair

Helicopter engines are often mounted atop the fuselage to keep the aircraft footprint small and optimal for operations. As a result, hot gases produced by the engines may inadvertently impinge upon the tail boom or dissipate inefficiently that compromises on operation safety. In this study, a scaled fuselage model with a hot air blower was used to simulate hot exhaust gases. The velocity field immediately outside the exhaust port was measured through stereoscopic particle image velocimetry to capture the trajectory and flow behaviour of the gases. Two cases were considered: freestream to exhaust velocity ratios of 0 (no freestream velocity) and 0.46 (co-flowing free stream), respectively. The formation of a counter-rotating vortex pair was detected for both cases but were opposite in the rotational sense. For the case without freestream, the plume formed into a small “kidney” shape, before expanding and dissipating downstream. For the case with freestream, the plume formed into a slenderer and more elongated “reversed-C” shape as compared to the case without freestream. It also retained its shape further downstream and maintained its relative position. These observations on the trajectory and shape of plume provide basis to understanding the nature and interaction of the plume with its surroundings.

Investigation of Film Cooling Using Time-Resolved Stereo Particle Image Velocimetry

2020 ◽  
Author(s):  
Katharina Stichling ◽  
Maximilian Elfner ◽  
Hans-Jörg Bauer
Keyword(s):  
Particle Image Velocimetry ◽  
Film Cooling ◽  
Particle Image ◽  
Density Ratio ◽  
Test Rig ◽  
Time Resolved ◽  
Hot Gas ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry ◽  
Cooling Air

Abstract In the present study an existing test rig at the Institute of Thermal Turbomachinery (ITS), Karlsruhe Institute of Technology (KIT) designed for generic film cooling studies is adopted to accommodate time resolved stereoscopic particle image velocimetry measurements. Through a similarity analysis the test rig geometry is scaled by a factor of about 20. Operating conditions of hot gas and cooling air inlet and exit can be imposed that are compliant with realistic engine conditions including density ratio. The cooling air is supplied by a parallel-to-hot gas coolant flow-configuration with a coolant Reynolds number of 30,000. Time-resolved and time-averaged stereo particle image velocimetry data for a film cooling flow at high density ratio and a range of blowing ratios is presented in this study. The investigated film cooling hole constitutes a 10°-10°-10° laidback fan-shaped hole with a wide spacing of P/D = 8 to insure the absence of jet interaction. The inclination angle amounts to 35°. The time-resolved data indicates transient behaviour of the film cooling jet.

Flow Pattern Measurements by µ-PIV in the Microchannels of a Heat Exchanger and Solutions to the Particle Fouling Problem

2004 ◽  
Author(s):  
V. Heinzel ◽  
A. Jianu ◽  
H. Sauter
Keyword(s):  
Heat Exchanger ◽  
Particle Image ◽  
Field Measurements ◽  
Velocity Fields ◽  
Particle Image Velocimetry System ◽  
The Past ◽  
Image Velocimetry ◽  
Test Loop ◽  
Transparent Liquid ◽  
Flat Cell

Preliminary experimental results of measuring velocity fields of a transparent liquid flow in a closed circuit, through a 100 μm deep flat cell with heat exchanger microchannel elements are presented. The resolution and possible errors of the microscopic particle image velocimetry system are discussed in relation with the evaluation results. Particle fouling phenomenon, which proved to be the main difficulty in performing velocity field measurements in microchannels in the past, are widely overcome by techniques which avoid or limit it. The test object, which is aimed at being exposed to real technical conditions (pressures up to 0.6 MPa leading to flow velocities up to 15 m/s, as well as temperatures up to 100°C), was up to now operated at a Reynolds number of about 5. The obtained information allows for starting the test loop upgrade.

scholarly journals Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets

2011 ◽  
Vol 676 ◽  
pp. 461-490 ◽  
Author(s):  
FABRICE SCHLEGEL ◽  
DAEHYUN WEE ◽  
YOUSSEF M. MARZOUK ◽  
AHMED F. GHONIEM
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Near Field ◽  
Vortex Pair ◽  
Transverse Jets ◽  
Vortical Structures ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Jet Trajectory ◽  
Counter Rotating Vortex Pair

Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.

scholarly journals Investigation of Film Cooling Using Time-Resolved Stereo Particle Image Velocimetry

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Katharina Stichling ◽  
Maximilian Elfner ◽  
Hans-Jörg Bauer
Keyword(s):  
Particle Image Velocimetry ◽  
Film Cooling ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Test Rig ◽  
Time Resolved ◽  
Hot Gas ◽  
Image Velocimetry ◽  
Cooling Air

Abstract In the present study, an existing test rig at the Institute of Thermal Turbomachinery (ITS), Karlsruhe Institute of Technology (KIT), designed for generic film cooling studies is adopted to accommodate time-resolved stereoscopic particle image velocimetry (SPIV) measurements. Through a similarity analysis, the test rig geometry is scaled by a factor of about 20. Operating conditions of hot gas and cooling air inlet and exit can be imposed that are compliant with realistic engine conditions including density ratio (DR). The cooling air is supplied by a parallel-to-hot gas coolant flow-configuration with a coolant Reynolds number of 30, 000. Time-resolved and time-averaged stereo article image velocimetry data for a film cooling flow at high DR and a range of blowing ratios are presented in this study. The investigated film cooling hole constitutes a 10 deg–10 deg–10 deg laidback fan-shaped hole with a wide spacing of P/D = 8 to insure the absence of jet interaction. The inclination angle amounts to 35 deg. The time-resolved data indicate transient behavior of the film cooling jet.

Analysis of Flow Physics and Jet-Mainstream Interaction in Leading Edge Filmcooling Using Large Eddy Simulation

2006 ◽  
Author(s):  
Ali Rozati ◽  
Danesh K. Tafti
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Low Frequency ◽  
Vortex Pair ◽  
Leading Edge ◽  
Windward Side ◽  
Stagnation Line ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Counter Rotating Vortex Pair

A numerical investigation is conducted to study leading edge film cooling at a compound angle with Large Eddy Simulation (LES). The domain geometry is adopted from an experimental set-up (Ekkad et al. [14]) where turbine blade leading edge is represented by a semi-cylindrical blunt body. The leading edge has two rows of coolant holes located at ±15° of the stagnation line. Coolant jets are injected into the flow field at 30° (spanwise) and 90° (streamwise). Reynolds number of the mainstream is 100,000 and jet to mainstream velocity and density ratios are 0.4 and 1.0, respectively. The results show the existence of an asymmetric counter-rotating vortex pair in the immediate wake of the coolant jet. In addition to these primary structures, vortex tubes on the windward side of the jet are convected downstream over and to the aft- and fore-side of the counter-rotating vortex pair. All these structures play a role in the mixing of mainstream fluid with the coolant. A turbulent boundary layer forms within 2 jet diameters downstream of the jet. A characteristic low frequency interaction between the jet and the mainstream is identified at a non-dimensional frequency between 0.79 and 0.95 based on jet diameter and velocity. The spanwise averaged adiabatic effectiveness agrees well with the experiments when fully-developed turbulence is used to provide time-dependent boundary conditions at the jet inlet, without which the calculated effectiveness is overpredicted.

Large-eddy simulations of a round jet in crossflow

1999 ◽  
Vol 379 ◽  
pp. 71-104 ◽  
Author(s):  
LESTER L. YUAN ◽  
ROBERT L. STREET ◽  
JOEL H. FERZIGER
Keyword(s):  
Coherent Structures ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Back Side ◽  
Round Jet ◽  
Turbulent Statistics ◽  
Jet Trajectory ◽  
Large Eddy ◽  
Crossflow Velocity ◽  
Counter Rotating Vortex Pair

This paper reports on a series of large-eddy simulations of a round jet issuing normally into a crossflow. Simulations were performed at two jet-to-crossflow velocity ratios, 2.0 and 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow velocity and jet diameter. Mean and turbulent statistics computed from the simulations match experimental measurements reasonably well. Large-scale coherent structures observed in experimental flow visualizations are reproduced by the simulations, and the mechanisms by which these structures form are described. The effects of coherent structures upon the evolution of mean velocities, resolved Reynolds stresses, and turbulent kinetic energy along the centreplane are discussed. In this paper, the ubiquitous far-field counter-rotating vortex pair is shown to originate from a pair of quasi-steady ‘hanging’ vortices. These vortices form in the skewed mixing layer that develops between jet and crossflow fluid on the lateral edges of the jet. Axial flow through the hanging vortex transports vortical fluid from the near-wall boundary layer of the incoming pipe flow to the back side of the jet. There, the hanging vortex encounters an adverse pressure gradient and breaks down. As this breakdown occurs, the vortex diameter expands dramatically, and a weak counter-rotating vortex pair is formed that is aligned with the jet trajectory.

Influence of Laser Drilling Imperfection on Film Cooling Performances

2005 ◽  
Author(s):  
Milenko B. Jovanovic´ ◽  
Hendrik C. de Lange ◽  
Anton A. van Steenhoven
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Particle Image ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Vortical Structures ◽  
Liquid Crystal Thermography ◽  
Image Velocimetry

Film cooling is studied on a jet in a cross-flow. The influence of a hole production imperfection on the jet-cross flow interaction is investigated experimentally by means of particle image velocimetry and liquid crystal thermography. To simulate the imperfection a half torus was placed inside the hole. The experiments were conducted with and without the production imperfection and the velocity ratio was varied. If the imperfection is absent, vortices are generated by means of the Kelvin-Helmholtz instability and separation on the hole trailing edge. The imperfection produces additional vortical structures and the flow field starts to oscillate. The deteriorated flow field changes the heat transfer. Surface temperature measurements show that the production imperfection reduces the film cooling effectiveness. The influence of the production imperfection on the film cooling effectiveness decreases with the enhanced velocity ratio.

scholarly journals Swarming bacterial fronts: Dynamics and morphology of active swarm interfaces propagating through passive frictional domains

2020 ◽  
Author(s):  
Joshua Tamayo ◽  
Yuchen Zhang ◽  
Merrill E Asp ◽  
Alison E Patteson ◽  
Arezoo M Ardekani ◽  
...  
Keyword(s):  
Particle Image ◽  
Wide Spectrum ◽  
Structural Features ◽  
Surface Dynamics ◽  
Steric Interactions ◽  
Correlation Lengths ◽  
Agent Based ◽  
Bacterial Films ◽  
Image Velocimetry ◽  
Surface Fluctuations

Swarming, a multicellular mode of flagella-based motility observed in many bacteria species, enables coordinated and rapid surface translocation, expansion and colonization. In the swarming state, bacterial films display several characteristics of active matter including intense and persistent long-ranged flocks and strong fluctuating velocity fields with significant vorticity. Swarm fronts are typically dynamically evolving interfaces. Many of these fronts separate motile active domains from passive frictional regions comprised of dead or non-motile bacteria. Here, we study the dynamics and structural features of a model active-passive interface in swarming Serratia marcescens. We expose localized regions of the swarm to high intensity wide-spectrum light thereby creating large domains of tightly packed immotile bacteria. When the light source is turned off, swarming bacteria outside this passivated region advance into this highly frictional domain and continuously reshape the interphase boundary. Combining results from Particle Image Velocimetry (PIV) and intensity based image analysis, we find that the evolving interface has quantifiable and defined roughness. Correlations between spatially separated surface fluctuations and damping of the same are influenced by the interaction of the interphase region with adjacently located and emergent collective flows. Dynamical growth exponents characterizing the spatiotemporal features of the surface are extracted and are found to differ from classically expected values for passive growth or erosion. To isolate the effects of hydrodynamic interactions generated by collective flows and that arising from steric interactions, we propose and analyze agent-based simulations with full hydrodynamics of rod-shaped, self-propelled particles. Our computations capture qualitative features of the swarm and predict correlation lengths consistent with experiments. We conclude that hydrodynamic and steric interactions enable different modes of surface dynamics, morphology and thus front invasion.

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